Brotato

To win any run, you have to make it through wave 20. Either beat the boss, or make it all the way to the end of the round without dying. To unlock hunter, you'll first need to get your range to 300 in a run (use Ranger, it's not too bad if that's what you're going for).

I should mention the sliders that allow you to nerf the enemies' health, damage, etc. Reportedly using these does not affect achievements, so use those if you are having problems.

I found Hunter somewhat difficult until I tried the crossbow. You'll want to improve your crit chance, but watch that you don't get it too high - look at your actual weapons to see their crit chance. Anything over 100% is obviously just wasted material/upgrades. You'll also need to improve attack speed. Range should be your first priority, since it also gives you damage, and ranged damage is next. Upgrading your crossbows is vital - each new tier adds another pierce. Hunter's Trophy is an automatic purchase.

You might be tempted to go for a lot of healing, and you probably want some, but really if you build enough damage and attack speed, you'll be killing everything before it reaches you. Get a bit of armor (around 6 or so), and if dodge or HP regen or even life steal presents itself then get it when you don't have better options. But really, you're trying to boost your damage to the point where it doesn't matter.